(1) Field of the Invention
The present invention relates to a tester and testing method for the detection of manufacturing defects produced in displays, and more particularly to a tester and testing method for the detection of open and short circuit defects in the signal lines of liquid crystal displays or the like.
(2) Description of the Related Art
Liquid crystal displays (LCDs) are becoming more and more popular and widely used in many types of electronic equipment including portable computers and portable data terminal devices. LCDs are made of a sandwich comprising upper and lower glass sheets with liquid crystal substrate sandwiched therebetween. The liquid crystal substrate typically comprise pixel electrodes for each pixel element, the pixel electrodes being arranged in an array pattern, gate lines, data lines, and thin film transistors (TFTs). As in other displays, the characters are built up from segments or dots formed from the pixel electrodes on the liquid crystal substrate.
LCDs typically undergo functional and other tests at the end of their manufacture to detect substrates having defective light segments or dots. Among the tests normally performed is an open/short circuit test to detect open and short circuits in display signal lines. Generally, the open/short circuit test measures the current or the resistance of each signal line after applying a voltage common to the signal lines. In this manner, defective LCDs are identified before being allowed to continue in the manufacturing process. The result of this testing is improved product quality and decreased overall product cost.
In addition, the completed LCD panel may be visually inspected to identify panels having malfunctioning or missing elements. Visual testing, however, is time consuming and does not provide quantitative data necessary for manufacturing process improvement.
A conventional open/short circuit tester and testing method are described below with reference to the accompanying drawings. As shown in FIG. 1, LCDs typically comprise a rectangular array or matrix having gate lines G1 to Gj running in a horizontal direction and data lines D1 to Di running at a vertical direction. Data lines D1 to Di cross gate lines G1 to Gi at predetermined intervals. At each cross point, a thin film transistor (TFT) (not shown in FIG. 1) and a pixel electrode is formed (not shown in FIG. 1). In an LCD, a picture is displayed in active area 100 comprising the rectangular array of TFTs and pixel electrodes.
In a conventional LCD, testing pads are included to facilitate testing for open and short circuits in the active area. First common pad 10 is connected to a first end of data lines D1 to Di. A plurality of testing pads 11 to 1i are connected to respective second ends of each data line d1 to Di. Likewise, a second common pad 20 is connected to a first end of gate lines G1 to Gi. A plurality of testing pads 21 to 2j are connected to a respective second ends of each gate line 21 to 2j. First common pad 10, second common pad 20, and testing pads 11 to 1i and 21 to 2j are typically located outside active area 100.
Testing for open and short circuits in the active area 100 is accomplished by probing the test pads in the following manner. A first and a second voltage is applied to first and second common pads 10 and 20, respectively, thereby applying a common first and second voltage to data lines D1 to Di and gate lines G1 to Gj, respectively. Testing pads 11 to 11i and 21 and 2j are then probed to measure the current and/or the resistance of each of the data and gate lines 11 to 1i and 21 to 2j.
The above-mentioned technique for open and short circuit testing is disadvantageous for several reasons. Testing in this manner is time consuming and costly because of the large number of testing pads involved. Moreover, as the resolution of LCDs increases, the pitch between the testing pads decreases. This, in turn, leads to a decrease in testing reliability because it is more difficult for the testing probe to make reliable contact with the testing pads.